"Black Dog" is a song by English rock band Led Zeppelin, which was released as the lead-off track of their untitled fourth album in 1971. It was released as a single in the US and Australia with Misty Mountain Hop on the B-side, and reached #15 on Billboard and #11 in Australia.
The sounds at the beginning are those of Jimmy Page warming up his electric guitar. He called it "waking up the army of guitars"—which are multitrack recorded in unison with electric bass guitar to provide the song's signature riff.
Led Zeppelin bass player John Paul Jones, who is credited with writing the main riff, got the idea for "Black Dog" after hearing Muddy Waters' experimental psychedelic-blues album, Electric Mud. He wanted to try "electric blues with a rolling bass part." The start-and-stop a cappella verses were inspired by Fleetwood Mac's 1969 song "Oh Well."